The invention relates to a method and an apparatus for demodulating time-discrete sampled frequency-modulated signals wherein samples of the signal to be demodulated are combined in such a way that the instantaneous frequency of the signal to be demodulated can be inferred from the output signal.
Digital signal processing makes it possible to tackle digitally numerous problems of signal processing which have previously been solved in analog technology. However, there are several exceptions. Thus, heretofore, in connection with demodulators for frequency-modulated signals (FM signals) used in analog technology, no corresponding digital component has been described which could carry out the function of FM demodulation at reasonable cost and in real time. Several possibilities resembling digital methods have proved unsuitable in practice. Thus, zero-crossing detectors are not very suitable, because the zero crossings are lost due to the necessarily performed sampling process. The desirable procedure would therefore be processing of the sampled values with the functions of an FM demodulator, while effects of amplitude modulation are suppressed or limited.
Specifically, several possibilities exist for the demodulation of time-discrete frequency-modulated signals: